STUDY OF THE ABSORPTION, EXCRETION, METABOLISM, AND RESIDUES IN TISSUES IN RATS TREATED WITH CARBON-14-LABELED PENDIMETHALIN, PROWL HERBICIDE

The metabolism of the dinitroaniline herbicide pendimethalin, PROWL herbicide [N-(l-ethylpropyl)- 3,4-dimethyl-2,6-dinitrobenzenamine], was investigated in rats by using [14C]-4-methyl-labeled pen dimethalin and [14C]-N-l-ethyl-labeled pendimethalin. Rats excreted radioactivity rapidly both in urine and especially in feces at two dosage levels, 7.3 and 37 mg/kg, of [14C]-4-methyl-labeled pendimetha lin. After 96 h, the residues were less than 0.3 ppm in all tissues except fat, which had a residue of 0.9 ppm. The major metabolic routes of pendimethalin involved hydroxylation of the 4-methyl and the N-1-ethyl group, oxidation of these alkyl groups to carboxylic acids, nitro reduction, cyclization, and conjugation based on the identification of the 12 metabolites in urine and the tissues. Products of cy clization reactions giving methylbenzimidazolecarboxylic acids were unique to liver and kidney. All the major metabolites retained both 14C labels of pendimethalin, indicating that N-dealkylation of the isopentyl group of pendimethalin was not significant. Metabolites with one or both nitro groups of pendimethalin reduced and with one or both nitro groups of 3,4-dimethyl-2,6-dinitrobenzenamine reduced were not detected in the urine, feces, and tissues. © 1990, American Chemical Society. All rights reserved.